U.S. patent number 5,232,792 [Application Number 07/934,005] was granted by the patent office on 1993-08-03 for cell separator plate used in fuel cell stacks.
This patent grant is currently assigned to M-C Power Corporation. Invention is credited to Gennady L. Reznikov.
United States Patent |
5,232,792 |
Reznikov |
August 3, 1993 |
Cell separator plate used in fuel cell stacks
Abstract
A cell separator plate for separating fuel cell units in fuel
cell stacks, the separator plate having a peripheral seal structure
extending from each face completely around its periphery and a
electrolyte seal structure extending from each face and having a
generally flat face spaced inwardly from the separator plate
peripheral seal structure and extending completely around the
separator plate forming a separator plate/electrolyte seal with an
adjacent electrolyte under cell operating conditions, and a
peripheral compartment between the separator plate/electrolyte seal
and separator plate peripheral seal between adjacent separator
plates. The peripheral compartment may contain active electrolyte
which may be wicked into the electrolyte matrix through edges of
the matrix directly exposed to the peripheral compartment. The
peripheral compartment may contain an inert gas to ensure active
electrolyte containment within the electrolyte matrix.
Inventors: |
Reznikov; Gennady L. (Niles,
IL) |
Assignee: |
M-C Power Corporation (Burr
Ridge, IL)
|
Family
ID: |
25464795 |
Appl.
No.: |
07/934,005 |
Filed: |
August 21, 1992 |
Current U.S.
Class: |
429/423; 429/458;
429/469; 429/478 |
Current CPC
Class: |
H01M
8/2483 (20160201); H01M 8/0206 (20130101); H01M
8/244 (20130101); H01M 8/0271 (20130101); H01M
8/0625 (20130101); H01M 8/04283 (20130101); Y02E
60/50 (20130101); H01M 8/021 (20130101); H01M
8/0228 (20130101); H01M 2300/0051 (20130101); H01M
2008/147 (20130101); Y02E 60/526 (20130101); H01M
8/0202 (20130101) |
Current International
Class: |
H01M
8/24 (20060101); H01M 8/02 (20060101); H01M
8/06 (20060101); H01M 8/04 (20060101); H01M
8/14 (20060101); H01M 002/08 (); H01M 008/04 () |
Field of
Search: |
;429/35,14,18,34,38,39 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Skapars; Anthony
Attorney, Agent or Firm: Speckman, Pauley & Fejer
Claims
I claim:
1. In a fuel cell stack comprising a plurality of fuel cell units,
each said fuel cell unit comprising an anode, a cathode, an
electrolyte in contact on one side with the electrolyte facing face
of said anode and in contact on the opposite side with the
electrolyte facing face of said cathode, and a separator plate
forming an anode chamber between the anode facing face of said
separator plate and said separator plate facing face of said anode
and said separator plate forming a cathode chamber between the
opposite cathode facing face of said separator plate and the
separator plate facing face of the cathode of an adjacent said fuel
cell unit, said anode chamber in gas communication with fuel gas
supply and outlet and said cathode chamber in gas communication
with oxidant supply and outlet, the improvement comprising; said
electrolyte terminating inwardly from the periphery of said
separator plate, said separator plate having a electrolyte seal
structure extending outwardly from each face, said electrolyte seal
structure contacting the periphery of said electrolyte completely
around the periphery of said electrolyte forming a separator
plate/electrolyte seal under cell operating conditions, said
separator plate extending beyond the periphery of said electrolyte
and having a separator plate peripheral seal structure spaced
beyond the periphery of said electrolyte and extending outwardly
from each face of said separator plate, and sealing means at said
separator plate peripheral seal structure to form with adjacent
separator plates when in said fuel cell stack a peripheral
separator plate seal completely around the periphery of said
separator plate thereby forming a peripheral compartment between
said separator plate/electrolyte seal and said peripheral separator
plate seal.
2. In a fuel cell stack according to claim 1 wherein end plates of
said fuel cell stack are configured the same as the corresponding
separator plate face on their inner faces and form half cells on
each end of said fuel cell stack.
3. In a fuel cell stack according to claim 1 wherein each said
separator plate is a pressed metal plate about 0.010 to about 0.050
inch thick.
4. In a fuel cell stack according to claim 1 wherein said separator
plate peripheral seal structure and said electrolyte seal structure
on one face of each said separator plate comprises a pressed
shaping of said plate to form said peripheral seal structure and
said electrolyte seal structure extending from said one face and on
the other face of said separator plate comprises a pressed sheet
metal shape fastened to said other face to form said peripheral
seal structure and said electrolyte seal structure extending from
said other face.
5. In a fuel cell stack according to claim 1 wherein said separator
plate peripheral seal structure and said electrolyte seal structure
comprise a pressed sheet metal shape fastened to at least one face
of said separator plate.
6. In a fuel cell stack according to claim 1 wherein said separator
plate/electrolyte seal is a wet seal.
7. In a fuel cell stack according to claim 6 wherein the width of
said wet seal is about 1/4 to about 3/4 inch.
8. In a fuel cell stack according to claim 1 wherein the width of
said separator plate/electrolyte seal is less than about 1
inch.
9. In a fuel cell stack according to claim 1 wherein each said
separator plate on said anode facing face is coated or clad with a
metal selected from the group consisting of nickel and copper.
10. In a fuel cell stack according to claim 1 wherein said
electrolyte comprises alkali metal carbonates.
11. In a fuel cell stack according to claim 1 additionally
comprising a current collector between each said anode and said
separator plate and each said cathode and said separator plate.
12. In a fuel cell stack according to claim 1 wherein said sealing
means comprises a sealing strip more resilient than the matrix of
said electrolyte.
13. In a fuel cell stack according to claim 1 wherein said
peripheral compartment contains active electrolyte supply which may
be wicked into electrolyte matrix through edges of said electrolyte
matrix directly exposed to said peripheral compartment.
14. In a fuel cell stack according to claim 1 wherein said
peripheral compartment contains an inert gas.
15. In a fuel cell stack according to claim 1 wherein said
electrolyte and said separator plate each has a plurality of
aligned perforations, each of said perforations in said separator
plate being surrounded by a flattened manifold seal structure
extending from each face of said separator plate, said manifold
seal structure having a width to contact less than about 1 inch
width of one of said electrolyte forming separator
plate/electrolyte manifold seals less than about 1 inch width under
cell operating conditions to form a plurality of gas manifolds
extending through said cell stack, conduits through extended
manifold seal structures of one set of manifolds on said anode
facing face providing fuel and exhaust gas communication between
said one set of manifolds and said anode chambers, and conduits
through extended manifold seal structures of a second set of
manifolds on said cathode facing face providing oxidant and exhaust
gas communication between said second set of manifolds and said
cathode chambers, thereby providing fully internal manifolding of
fuel and oxidant gases to and from each said unit fuel cell in said
fuel cell stack.
16. In a fuel cell stack according to claim 1 wherein said fuel
cell stack has interspersed along its axis a plurality of reforming
chambers each formed by two separator/reformer plates, one having
the configuration of said anode facing face and the second having
the configuration of said cathode facing face, said two separator
plates sealingly joined in their edge area to enclose a reformer
chamber, supply means providing reaction gas and steam to said
reformer chamber, and hydrogen product withdrawal means in
communication with said fuel gas supply.
17. In a fuel cell stack according to claim 1 wherein said cell
stack end plates are configured the same as said separator plate on
their corresponding inner faces and form half cells on each end of
said fuel cell stack, said separator plate is pressed metal about
0.010 to about 0.050 inch thick, said separator plate peripheral
seal structure and said electrolyte seal structure comprise a
pressed sheet metal shape fastened to at least one face of said
separator plate, and said electrolyte comprises alkali metal
carbonates.
18. In a fuel cell stack according to claim 17 wherein said sealing
means comprises a sealing strip more resilient than the matrix of
said electrolyte and said peripheral compartment contains active
electrolyte supply which may be wicked into electrolyte matrix
through edges o said electrolyte matrix directly exposed to said
peripheral compartment.
19. A fuel cell separator plate comprising a thin metallic plate
having a separator plate peripheral seal structure extending from
each face of said metallic plate completely around its periphery
and a electrolyte seal structure extending from each face of said
metallic plate and having a generally flat face spaced inwardly
from said separator plate peripheral seal structure and extending
completely around said metallic plate in said inwardly spaced
relation, said generally flat face capable of forming a separator
plate/electrolyte seal with an adjacent electrolyte under cell
operating conditions.
20. A fuel cell separator plate according to claim 19 wherein said
metallic plate is pressed metal about 0.010 to about 0.050 inch
thick.
21. A fuel cell separator plate according to claim 19 wherein said
separator plate peripheral seal structure and said electrolyte seal
structure comprise a pressed sheet metal shape fastened to at least
one face of said separator plate.
22. A fuel cell separator plate according to claim 19 wherein said
separator plate/electrolyte seal is a wet seal.
23. A fuel cell separator plate according to claim 22 wherein the
width of said generally flat face is about 1/4 to about 3/4
inch.
24. A fuel cell separator plate according to claim 19 wherein the
width of said generally flat face is less than about 1 inch.
25. A fuel cell separator plate according to claim 19 wherein the
anode facing face is coated or clad with a metal selected from the
group consisting of nickel and copper.
26. A process for adding make-up active electrolyte to a fuel cell
unit in a fuel cell stack comprising; storing said make-up active
electrolyte in a peripheral compartment formed by adjacent
separator plates between a separator plate/electrolyte seal around
the periphery of the electrolyte matrix and a separator plate
peripheral seal around the periphery of adjacent separator plates
spaced outwardly from said separator plate/electrolyte seal, and
passing said make-up active electrolyte from said peripheral
compartment into said electrolyte matrix through the edges of said
electrolyte matrix directly exposed to said peripheral
compartment.
27. In the process for adding make-up active electrolyte according
to claim 26 wherein said separator plate/electrolyte seal is a wet
seal less than about 1 inch width.
28. In the process for adding make-up active electrolyte according
to claim 26 wherein said electrolyte comprises alkali metal
carbonates.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to high temperature fuel cell stacks,
particularly molten alkali metal carbonates fuel cell stacks using
thin metal separator plates. The separator plates of this invention
provide improved electrolyte containment and may provide make-up
electrolyte during cell operation.
2. Description of Related Art
Generally, fuel cell electrical output units are comprised of a
stacked multiplicity of individual cells separated by inert or
bi-polar electronically conductive ferrous metal separator plates.
Individual cells are sandwiched together and secured into a single
stacked unit to achieve desired fuel cell energy output. Each
individual cell generally includes an anode and cathode electrode,
a common electrolyte tile, and a fuel and oxidant gas source. Both
fuel and oxidant gases are introduced through manifolds to their
respective reactant chambers between the separator plate and the
electrolyte tile. The area of contact between the electrolyte and
other cell components to maintain separation of the fuel and
oxidant gases and prevent and/or minimize gas leakage is known as
the wet seal. A major factor attributing to premature fuel cell
failure is corrosion and fatigue in the wet seal area. This failure
is hastened by corrosive electrolyte contact at high temperatures
and high thermal stresses resulting from large temperature
variations during thermal cycling of the cell causing weakening of
the structure through intracrystalline and transcrystalline
cracking. Such failures permit undesired fuel and/or oxidant gas
crossover and overboard gas leakage which interrupts the intended
oxidation and reduction reactions thereby causing breakdown and
eventual stoppage of cell current generation. Under high
temperature fuel cell operating conditions, in the range of about
500.degree. to 700.degree. C., molten carbonate electrolytes are
very corrosive to ferrous metals which, due to strength
requirements, are necessary for fuel cell housings and separator
plates. The high temperature operation of stacks of molten
carbonate fuel cells increases both the corrosion and thermal
stress problems in the wet seal area, especially when the thermal
coefficients of expansion of adjacent materials are different.
Commercially viable molten carbonate fuel cell stacks may contain
up to about 600 individual cells each having a planar area in the
order of ten square feet. In stacking such individual cells,
separator plates separate the individual cells with fuel and
oxidant each being introduced between a set of separator plates,
the fuel being introduced between one face of a separator plate and
the anode side of an electrolyte matrix and oxidant being
introduced between the other face of the separator plate and the
cathode side of a second electrolyte matrix. The problems of
manifolding and sealing become more severe when larger number of
cells and larger planar areas are used in the cell stack. When
greater number of cells are used, the electrical potential driving
the carbonate in the seal area along the height of the stack
increases, and when the planar area of the cell increases, the
linear tolerances of each component and the side alignment of each
component becomes extremely difficult to maintain in order to
maintain the mating surface sealed between the manifold/manifold
gasket/and cell stack. Cell stacks containing 600 cells can be
approximately 10 feet tall presenting serious problems of required
stiffness of external manifolds and the application of a clamping
force required to force the manifold onto the cell stack. Due to
the thermal gradients between cell assembly and cell operating
conditions, differential thermal expansions, and the necessary
strength of materials used for the manifolds, close tolerances and
very difficult engineering problems are presented.
Conventionally, stacks of individual molten carbonate fuel cells
have been constructed with spacer strips around the periphery of a
separator plate to form wet seals and to provide intake and exhaust
manifolds. Various means of sealing in the environment of the high
temperature fuel cell wet seal area are disclosed in U.S. Pat. No.
4,579,788 teaching the wet seal strips are fabricated utilizing
powder metallurgy techniques; U.S. Pat. No. 3,723,186 teaching the
electrolyte itself is comprised of inert materials in regions
around its periphery to establish an inert peripheral seal between
the electrolyte and frame or housing; U.S. Pat. No. 4,160,067
teaching deposition of inert materials onto or impregnated into the
fuel cell housing or separator in wet seal areas; U.S. Pat. No.
3,867,206 teaching a wet seal between electrolyte-saturated matrix
and electrolyte saturated peripheral edge of the electrodes; U.S.
Pat. No. 4,761,348 teaching peripheral rails of gas impermeable
material to provide a gas sealing function to isolate the anode and
cathode from the oxidant and fuel gases, respectively; U.S. Pat.
No. 4,329,403 teaching graded electrolyte composition for more
gradual transition in the coefficient of thermal expansion in
passing from the electrodes to the inner electrolyte region; and
U.S. Pat. No. 3,514,333 teaching housing of alkali metal carbonate
electrolytes in high temperature fuel cells by use of a thin
aluminum sealing gasket.
Gas sealing of a phosphoric acid fuel cell, which operates at about
150.degree. to 220.degree. C., by filling the pores of a porous
material periphery of the cell constituents with silicon carbide
and/or silicon nitride is taught by U.S. Pat. No. 4,781,727; and by
impregnating interstitial spaces in substrate plate edge is taught
by U.S. Pat. Nos. 4,786,568 and 4,824,739. The solution of sealing
and corrosion problems encountered in low temperature electrolytic
cells, such as bonding granular inert material with
polytetrafluorethylene as taught by U.S. Pat. No. 4,259,389 gaskets
of polyethylene as taught by U.S. Pat. No. 3,012,086; and "O" ring
seals taught by U.S. Pat. No. 3,589,941 for internal manifolding of
fuel only are not suitable for high temperature molten carbonate
fuel cells.
U.S. Pat. No. 4,910,101 teaches fuel cell stacks having exterior
extensions on the separator plates to form receivers for surplus
electrolyte in a gas discharge manifold to the exterior of the fuel
cell stack and provides means for return of recovered electrolyte
to the same cell from which it leaked without substantial pressure
loss. The receivers on the separator plates also provides a method
for addition of electrolyte to the operating fuel cell.
U.S. Pat. Nos. 4,963,442 and 5,045,413 teach fully internal
manifolded fuel cell stacks wherein the electrolytes and separator
plates extend to the edge of the fuel cell stack and form a
peripheral wet seal by the separator plate having a flattened wet
seal structure extending from each face of the separator plate to
contact the electrolytes completely around their periphery to form
a separator plate/electrolyte wet seal under fuel cell operating
conditions. The electrolytes and separator plates each have a
plurality of aligned perforations, the perforations in the
separator plates each being surrounded by a flattened manifold wet
seal structure extending from each face of the separator plate to
contact the electrolytes to form a separator plate/electrolyte wet
seal under fuel cell operating conditions thereby providing a
plurality of manifolds extending through the fuel cell stack for
fully internal manifolding of fuel and oxidant gases to and from
each unit fuel cell in the fuel cell stack. U.S. Pat. No. 5,077,148
teaches a fully internal manifolded and internal reformed fuel cell
stack having separator plate/electrolyte seals similar to those
taught by U.S. Pat. Nos. 4,963,442 and 5,045,413 and having
interspersed along its axis a plurality of reforming chambers
formed by adjacent separator plates to provide fully internal
manifolding of reactant gas and steam to product gas from each
reformer unit in the fuel cell stack.
SUMMARY OF THE INVENTION
It is an object of this invention to provide high temperature fuel
cell stacks having increased long term stability as a result of
improved electrolyte sealing with reduced electrolyte loss and
reduced corrosion.
It is another object of this invention to provide high temperature
fuel cell stacks having an internal supply of make-up active
electrolyte.
It is still another object of this invention to provide molten
alkali metal carbonates electrolyte fuel cell stacks of high long
term stability and internal supply of make-up electrolyte.
These and other objects and advantages of the invention which will
become apparent upon reading the detailed description may be
achieved in fuel cell stacks of a plurality of fuel cell units,
each fuel cell unit having an anode, a cathode, an electrolyte in
contact on one side with the electrolyte facing face of the anode
and in contact on the opposite side with the electrolyte facing
face of the cathode, and a separator plate forming an anode chamber
between the anode facing face of the separator plate and the
separator plate facing face of the anode and a cathode chamber
between the opposite cathode facing face of the separator plate and
the separator plate facing face of the cathode of an adjacent fuel
cell unit. The anode chamber is in gas communication with fuel gas
supply and outlet and the cathode chamber is in gas communication
with oxidant supply and outlet. In each fuel cell unit according to
the present invention, the electrolyte terminates inwardly from the
periphery of the separator plate. The separator plate has an
electrolyte seal structure extending outwardly from each face, the
electrolyte seal structure having a width to contact, preferably
less than about 1 inch width, at the periphery of the electrolyte
completely around the periphery of the electrolyte forming a
separator/electrolyte seal, preferably less than 1 inch width,
under fuel cell operating conditions. The separator plate extends
beyond the periphery of the electrolyte and has a separator plate
peripheral seal structure spaced beyond the periphery of the
electrolyte seal structure and extending outwardly from each face
of the separator plate. Sealing means are provided at the separator
plate peripheral seal structure to form with an adjacent separator
plate peripheral seal structure, when in the fuel cell stack, a
peripheral separator plate seal completely around the periphery of
the separator plate thereby forming a peripheral compartment
between the separator plate/electrolyte seal and the peripheral
separator plate seal. In the fuel cell stack, the end plates are
configured the same as the corresponding separator plate face on
their inner faces and form half cells on each end of the fuel cell
stack.
In preferred embodiments, the separator plate/electrolyte seal is a
wet seal having a width of about 1/4 to about 3/4 inch. The
separator plate/electrolyte wet seal is preferably formed by molten
alkali metal carbonates electrolyte.
It is preferred that the separator plate is a pressed metal plate
about 0.010 to about 0.050 inch thick and that the separator plate
on the anode facing face is coated or clad with a metal selected
from nickel and copper.
In one embodiment, the separator plate peripheral seal structure
and electrolyte seal structure is formed by a single pressed metal
shape with one such shape fastened to at least one face of the
separator plate, and preferably to each face of the separator
plate.
In one embodiment, the separator plate peripheral seal structure
and electrolyte seal structure on one face of the separator plate
is a pressed shaping of the plate to form the separator plate
peripheral seal structure and electrolyte seal structure extending
outwardly from one face of the separator plate and on the other
face is a pressed sheet metal shape fastened to that other face to
form the separator plate peripheral seal structure and electrolyte
seal structure extending outwardly from that face.
It is preferred that the sealing means forming the separator plate
peripheral seal be more resilient than the matrix of the
electrolyte forming the separator plate/electrolyte wet seal.
The peripheral compartment between the separator plate/electrolyte
seal and the separator plate peripheral seal preferably contains
active electrolyte which may be wicked into the active volume
through the electrolyte matrix directly exposed to the peripheral
compartment. This make-up electrolyte which may be directly wicked
into each fuel cell unit from the corresponding peripheral
compartment makes up for any loss of electrolyte from the fuel cell
unit and provides greater fuel cell stack stability and duration of
operational time.
BRIEF DESCRIPTION OF THE DRAWING
The above objects and advantages of this invention will become
further apparent upon reading the detailed description of preferred
embodiments in reference to the drawing wherein:
FIG. 1 is a sectional view of a portion of the peripheral area of a
separator plate according to one embodiment of this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The fuel cell separator plates according to the present invention
are suitable for use in stacks of any type of fuel cell units
having planar components, especially high temperature fuel cells
such as molten alkali metal carbonates and solid conductor/solid
oxide fuel cells. Such fuel cell units and stacks together with
their components have been described in more detail in U.S. Pat.
Nos. 4,963,442, 5,045,413, and 5,077,148 which are incorporated
herein in their entirety by reference. These patents describe
suitable anode, cathode, current collector, electrolyte, and
separator plate components and their configurations, materials and
functioning which is the same as practiced in the present invention
except in the peripheral area as described below. The separator
plates of this invention are particularly suitable for use in fully
internally manifolded fuel cell stacks and in internal reformed
fuel cell stacks as described in the above patents. However, the
separator plates of this invention may be used in fuel cell stacks
of any shape or configuration having planar components.
This invention is concerned with the peripheral region of the
separator plates. The internal portion of the separator plate may
be of any configuration to promote good circulation of gases in the
anode and cathode compartments. For large separator plates, in the
order of 10,000 cm.sup.2 for commercial sized fuel cell stacks, it
may be desirable to provide multiple active areas on the face of
the separator plate, but this does not alter the peripheral regions
as described in the present invention. The separator plates of this
invention may be used with any configuration of the separator plate
for internal manifolding and/or internal reforming. Likewise, the
mounting of electrodes may be varied from that shown in the
Figures.
Separator plates may be comprised of suitable materials providing
desired physical strength and gas separation. The separator plates
are desirably very thin, about 0.010 to about 0.050 inch thick,
preferably about 0.015 to about 0.025 inch thick. In many cell
stacks it is preferred to use bimetallic separator plates in which
stainless steel may be used on the cathode face and nickel or
copper on the anode face to avoid ferrous metal corrosion. The
nickel or copper may be a cladding, lamination or plating about 10
percent the thickness of the separator plate. Separator plates may
also be fabricated from ferrous alloys, such as type 300 series
stainless steel alloys. The separator plates provide the dual
function of providing a gas chamber non-reactive separator as well
as providing structural strength to the fuel cell as an internal
load bearing member. While it is preferred to use separator plates
having a corrugated and/or dimpled cross-sectional shape in the
active area to provide both strength and better gas circulation
adjacent the electrodes, the principles of this invention are also
applicable to flat separator plates structured to provide
peripheral seal areas and to provide seals around internal manifold
holes while allowing gas to pass to and from the internal manifolds
as required for fuel cell operation. Thin stamped stainless steel
plates suitable for use in this invention are similar in the active
area to those used in heat exchange technology as described in the
publications "Modern Designs For Effective Heat Transfer," American
Heat Reclaiming Corp., 1270 Avenue of the Americas, New York, N.Y.
10020, and "Supercharger Plate and Frame Heat Exchanger," Tranter,
Inc. Wichita Falls, Tex. 76307.
As shown in FIGS. 1 and 2 of each of the U.S. Pat. Nos. 4,963,442
and 5,077,148, electrolyte 20 and separator plate 40 extend to the
outer edge of the cell and are sealed to each other around their
periphery in wet seal areas 23. The individual molten carbonate
fuel cell unit is shown with anode 26 spaced from one face of
separator plate 40 to provide an anode chamber fed by fuel manifold
hole 24 as indicated by arrow 38. On the other face of separator
plate 40 cathode 27 is spaced from separator plate 40 to form a
cathode chamber in communication with oxidant manifold holes 25 as
indicated by arrow 39. Electrolyte 20 and separator plate 40 extend
to the outer edge of the cell forming peripheral wet seal areas 23
which provide peripheral wet seals between the electrolyte and
separator plate for containment of fluid. Fuel manifold wet seal
area 45 and oxidant wet seal area 46 provide manifold sealing by
electrolyte/separator plate wet seals and provide desired guidance
of fluid to anode and cathode chambers on opposite sides of
separator plate 40. No additional gaskets are used for sealing and
the cell unit can accommodate a wide variety of carbonate addition
techniques, including use of carbonate tapes. In the present
invention, the active cell areas, the internal manifolds, and
internal reforming may be the same as described in these patents.
The present invention relates to double sealing arrangements, an
electrolyte/separator plate seal at the periphery of the
electrolyte and spaced beyond the periphery of the electrolyte a
separator plate/separator plate seal at the periphery of the
separator plates forming a peripheral compartment therebetween.
FIG. 1 is one embodiment of this invention, not drawn to scale,
showing in detail a peripheral area of fuel cell unit 10 in
accordance with one embodiment of this invention. Fuel cell unit 10
components are drawn in solid lines and partial components of
adjacent fuel cell units are drawn in dashed lines. Thin sheet
separator plate 20 is corrugated with the peaks on anode facing
face 23 of separator plate 20 adjacent anode 13 current collector
15 forming anode chambers 16 while peaks on cathode facing face 24
of separator plate 20 adjacent cathode 12' current collector 14, of
an adjacent fuel cell unit form cathode chambers 17. Electrolyte 11
terminates with end 18 inwardly from the periphery of separator
plate 20 as shown in FIG. 1. By periphery of the separator plate is
meant the termination of the plate structure beyond the separator
plate peripheral seal including any seal structure attached to the
separator plate structure itself. Separator plate 20 has
electrolyte seal structure 21 extending outwardly from one face and
electrolyte seal structure 31 extending outwardly from its opposite
face sized to contact electrolyte 11 completely around the
electrolyte periphery to form a separator plate/electrolyte seal
under cell operating conditions. By the terminology "extending
outwardly" from a face of the separator plate as used throughout
this description and claims is meant outwardly from a generally
flat separator plate extending through the central region of and
parallel to the shaped separator plates used in this invention.
Separator plate 20 extends beyond the periphery of electrolyte 11
and has separator plate peripheral seal structure 22 extending
outwardly from one face and separator plate peripheral seal
structure 32 extending outwardly from its opposite face. The
separator plate peripheral seal structures and electrolyte seal
structures may be obtained in a variety of ways and this invention
is intended to include all configurations and manners of fastening
such structures to the separator plate as long as a separator
plate/electrolyte seal is formed at the periphery of the
electrolyte and a separator plate/separator plate seal is formed at
the periphery of adjacent separator plates to form a peripheral
compartment therebetween with end 18 of the electrolyte in
communication with that compartment. FIG. 1 shows separator plate
20 extending as a generally flat plate from the active area of the
cell to the periphery of the cell with a separate structure forming
electrolyte seal structure 21 and separator plate peripheral seal
structure 22 fastened to one face and a second separate structure
forming electrolyte seal structure 31 and separator plate
peripheral seal structure 32 fastened to the opposite face of
separator plate 20. Separator plate 20 may be pressed to form the
electrolyte seal structure and separator plate peripheral seal
structure extending from one face while a pressed sheet metal shape
having the desired electrolyte seal structure and separator plate
peripheral seal structure is fastened to the opposite face of
separator plate 20 to form the electrolyte seal structure and
peripheral seal structure extending outwardly from the opposite
face of separator plate 20. In each of these specific embodiments,
the electrolyte seal structure and separator plate peripheral seal
structure comprises a pressed sheet metal shape fastened to at
least one face of the separator plate. Such metal shapes may be
fastened to separator plate 20 by any suitable means known to the
metal fastening art, such as by welds 25. However, it is readily
apparent to one skilled in the art that the desired structure and
functions of a electrolyte/separator plate seal at the periphery of
the electrolyte and a separator plate/separator plate seal at the
periphery of adjacent separator plates providing a peripheral
compartment therebetween may be achieved by a number of different
structures which are included within this invention.
In one preferred embodiment of this invention, molten alkali metal
carbonates electrolyte is used and in this case it is preferred
that the separator plate/electrolyte seal is a wet seal as is known
in the art of molten carbonate fuel cells. The wet seals are formed
due to pressure from the upstanding wet seal areas on both faces of
the separator plates around the periphery of the electrolyte and
around each of any internal manifolds when the cell stack is
tightened together. Narrow wet seal areas have been found to
function better than wider ones. It is desired that the upstanding
wet seal areas be constructed of the same thin material as the
separator plate, about 0.010 to about 0.050 inch thick and
preferably about 0.015 to about 0.025 inch thick, with a flattened
wet seal contact width of less than about 1 inch in order to avoid
sagging and yielding which leads to leaking. Preferably, the width
of the flattened wet seal contact structure is about 0.25 to about
0.75 inch to avoid the necessity of internal bridging and supports.
Further, wet seals of up to about 1 inch wide provide required
complete removal of organic binders from green electrolyte matrix
tapes during cell heat-up to allow good carbonate electrolyte
retention in the electrolyte matrix. Wet seals wider than about 1
inch show indications of residual carbonaceous material and lesser
amounts of carbonate electrolyte which could lead to leaky wet seal
during cell operations. The cell unit according to this invention
can accommodate a wide variety of carbonate addition techniques,
including use of carbonate tapes. Similar wet seals may be formed
around each of the internal manifolds by similar upstanding
electrolyte seal structures on each side of the separator plate.
The porous electrodes may be filled with a higher melting material,
such as a brazing material, in the areas of the wet seals to
prevent leakage of the liquid electrolyte through the electrodes
under cell operating conditions.
When carbonate tapes are used, the carbonate tapes and electrolyte
matrix extend across the electrolyte/separator plate seal area and
although the inter-cell spacing decreases in proportion to the
thickness of the carbonate tapes when they melt, sealing and
conformity of all cell components is maintained at all times due to
the tightening force on the cell stack, the resiliency of the
electrolyte seal structure and the separator plate peripheral seal
structure and peripheral sealing means as will be further
explained. During cell heat-up prior to carbonate tape melting,
sealing is maintained because the carbonate tapes and the
electrolyte matrix, such as LiAlO.sub.2, extend adjacent to the
respective sealing surfaces and contain a rubbery binder. During
binder burn-out, which occurs prior to carbonate melt, gas flows
are maintained in manifolds and electrolyte or inert gas maintained
in the peripheral compartment which aids in maintaining sealing.
When the binder is burned off and the cell temperature raised to
the melting point of the carbonate, the melting carbonate is
absorbed by the porous LiAlO.sub.2 tape and the electrodes. The
inter-cell spacing decreases as the carbonate tapes melt but at all
stages from temperature to operating temperatures of about
650.degree. C. cell sealing is maintained. The limited flexibility
and resiliency of the thin sheet metal in the seal areas aids in
assuring maintenance of cell sealing.
The separator plate peripheral seal structure is spaced beyond end
18 at the periphery of electrolyte 11 and extends outwardly from
each face of the separator plate. As shown in FIG. 1 separator
plate seal structure 22 extends outwardly from one face of the
separator plate and separator plate seal structure 32 extends
outwardly from the opposite face of the separator plate and
peripheral compartment 27 is formed between the electrolyte seal
and the separator plate peripheral seal. The separator plate
peripheral seal structure may be any shape suitable to form a
resilient and tight seal completely around the periphery of the
separator plate. Preferably thin sheet metal is used to provide
desired resilient forms as described with respect to the
electrolyte seal structures. Any suitable sealing means may be used
between adjacent separator plate peripheral seal structures, such
as a suitably resilient material which withstands cell operating
temperatures shown as 26 in FIG. 1. It is desired that the
separator plate peripheral seal have greater resiliency than the
electrolyte seal to accommodate the loss of thickness of
electrolyte tapes upon cell operation, as described above.
Peripheral sealing means 26 may be fabricated from refractory
oxides, such as MgO or aluminates such as LiAlO.sub.2, and a
mixture of salts which are stable under cell operating conditions,
such as carbonates K.sub.2 CO.sub.3 /Li.sub.2 CO.sub.3 /Na.sub.2
CO.sub.3.
Peripheral compartment 27 may be filled with CO.sub.2 to assist in
electrolyte containment within each cell and may be filled with
make-up active electrolyte. Make-up active electrolyte can be
stored in peripheral compartment 27 and passed during cell
operation into the electrolyte matrix through edges 18 of the
electrolyte directly exposed to the peripheral compartment. When
electrolyte is stored in the peripheral compartment, the separator
plate peripheral seal may be a wet seal utilizing the
electrolyte.
While in the foregoing specification this invention has been
described in relation to certain preferred embodiments thereof, and
many details have been set forth for the purpose of illustration,
it will be apparent to those skilled in the art that the invention
is susceptible to additional embodiments and that certain of the
details described herein can be varied considerably without
departing from the basic principles of the invention.
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